Recently I came to know about https://www.membrane.io/, which also follows similar approach, but it looks like that is more for internal apps and small projects.
From a high level what we offer is similar -- durable and reliable compute.
There isn't a lot of public information about how they are built, but from what I can tell you're right -- their architecture is more oriented for small projects.
It looks like they store the entire JS heap in a SQLLite database. We store schematized state checkpoints in Postgres compatible database, which makes it so that we can scale up and allow interesting things like querying the previous states and time travel debugging, where you can actually step though previously run workflows.